The application generally relates to heat recovery. The application relates more specifically to a system and method and for recovering waste heat from a carbon dioxide capture process, and using the waste heat to dry a fossil fuel.
Carbon dioxide (CO2) gas is released into the atmosphere from various industrial facilities such as fossil fuel power stations and refuse incinerating plants. Although substantial reductions in emissions of CO2 could be achieved by increase in efficiency of energy conversion and utilization, such reductions may not be sufficient to achieve atmospheric CO2 stabilization. Therefore, efforts have been directed towards the capture and sequestration of the CO2 emitted by fossil fuel power stations.
One type of fossil fuel power station uses pulverized coal as a combustion source. The pulverized coal may have moisture contents varying from about 3% to about 50% by weight. In some instances, the pulverized coal may need drying before being efficiently combusted to produce heat. In these instances, the pulverized coal may be dried by using plant steam, furnace flue gases, or regenerative air heaters. Often, bituminous or sub-bituminous coals are dried in the pulverizers that reduce the particle size of the coal by the same air that is used to combust the pulverized coal. For example, flue gas may be flowed through a tubular or regenerative air heater to heat the primary air. For lower rank, higher moisture coals, the furnace flue gas may also be mixed with ambient air and supplied to a coal-drying unit. In the case of using steam heat in the coal-drying unit, steam supplies heat to a fluidized bed and acts as a fluidizing medium and drying medium. Another type of fossil fuel used by power stations is lignite, which is high in moisture content and often requires drying before combustion.
Various systems and methods have been developed to capture and reuse CO2 gas. For example, an ammonia based process has been developed that treats cooled flue gas with aqueous ammonia, which reacts with the CO2 in the flue gas to form ammonia carbonate or bicarbonate. The temperature of the material binding the captured CO2 can be increased to reverse the capture reaction to release the CO2 under pressure. In another example, various amine processes have been developed that treat flue gas with an aqueous amine solution in an absorption/stripping type of regenerative process to absorb the CO2 for later desorption and capture.
In these exemplary CO2 capture methods, and in other similar methods, the captured CO2 is compressed after regeneration for transportation and storage. The regeneration and compression of the CO2 results in a significant amount of waste heat.
What is needed is a system and method for recovering waste heat generated during a CO2 capture process, and in particular, a system and method for improving overall plant efficiency by recovering waste heat for other plant or facility operations such as coal drying.
Intended advantages of the disclosed systems and methods satisfy one or more of these needs or provides other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.